The effects of saralasin, indomethacin and a converting enzyme inhibitor (SQ 14,225), as well as changes in catecholamine excretion and diurnal levels of plasma renin activity, will be studied to investigate the hypertensive mechanisms involved in the acute, subacute and chronic phases of one-clip, two-kidney renovascular hypertension in conscious dogs during sodium-replete states. Sequential changes in fluid and electrolyte balance and the effect of indomethacin will also be studied during the off-set phase of established renovascular hypertension. Changes in the renin secretion rates of the two kidneys of hypertensive dogs bearing bilateral chronic indwelling renal venous cannulae will be assessed before and after saralasin administration.